1. Field of the Invention
The present invention relates to a light emitting element module. Particularly, the invention relates a light emitting element module in which a light emitting element, an optical fiber and an optical system inserted therebetween are formed integrally with each other.
2. Description of the Related Art
FIGS. 4A to 4D are diagrams for explaining a general method of mounting an optical system in a light emitting element module which is a subject of the present invention.
As shown in FIGS. 4A, in a light emitting element module as such a type, a light emitting element 3 is mounted, through a chip carrier 2, on a horizontal portion 1a of a substrate 1 having an L-shaped section as a whole. On the other hand, a through hole 1c is formed in a vertical portion 1b of the substrate 1 so that the light emitting element 3 is generally located at the center of the hole.
With respect to the light emitting element 3 mounted on the substrate 1 as mentioned above, a lens 6 for focusing light emitted from the light emitting element 3 is attached to the vertical portion of the substrate 1 through a cylindrical member 4 in a state that the lens 6 is held in a lens holder 5, as shown in FIG. 4B. The lens holder 5 itself has a cylindrical shape, and the outer diameter thereof is smaller than the inner diameter of the through hole 1c of the substrate 1. The cylindrical member 4 has a flange portion 4a having an outer diameter larger than the inner diameter of the through hole formed in the substrate 1, and a cylindrical holder support portion 4b having an inner diameter into which the lens holder 5 can be inserted.
The above-mentioned parts are assembled in the following process.
First, the lens holder 5 is inserted into the cylindrical member 4, and the flange portion 4a of the cylindrical member 4 is brought into contact with the vertical portion 1b of the substrate 1 so that the top end of the lens holder 5 is inserted into the through hole 1c of the substrate 1. At this time, the respective members are in a state that they can be moved relatively to each other. That is, if the lens holder 5 is moved inside the cylindrical holder 4, the distance between the light emitting element 3 and the lens 6 can be adjusted. Further, if the flange portion 4a of the cylindrical member 4 is slid on the surface of the vertical portion 1b of the substrate 1, the direction of a light beam which has passed the lens 6 can be adjusted. After the distance and the direction of the light beams are adjusted thus respectively, the members are fixed relative to each other. Consequently, the mounting of the lens 6 is completed. An assembly as shown in FIG. 4C is finished thus.
Generally, it is preferable in a light emitting element module that the light output of a light emitting element can be taken out in the form of an optical fiber output as much as possible.
FIG. 5 shows the relationship between a relative value of the optical fiber output and a change of the distance between a lens and a semiconductor lens.
As shown in the drawing, the distance which makes the optical fiber output maximum depends on the specifications of the optical system and the light emitting element, and the optical fiber output is reduced if the distance is out of the optimum distance.
In the above-mentioned conventional assembling method, it is possible to easily adjust the distance between the light emitting element 3 and the lens 6. However, if laser welding or the like is used for fixing the lens holder 5 and the cylindrical member 4 with each other, there is a case where the adjusted distance may be changed due to the thermal deformation of a welded portion. Therefore, even if the working of the adjustment is performed carefully, there is a case where the adjustment is not reflected on the characteristics of final products.
In addition, since it is necessary to make the through hole 1c of the substrate, the cylindrical member 4 and the lens holder slide on or rub with each other, it is necessary to provide a gap 20 particularly between the inner surface of the cylindrical member 4 and the outer surface of the lens holder 5 as shown in FIG. 6. Owing to this gap, the lens holder 5 may be fixed inside the cylindrical member 4 with an inclination. Accordingly, it results in deterioration of the characteristics of final products.
As described above, in the configuration of a conventional light emitting element module and the assembling method therefor, the result of the adjustment performed at the time of assembling is not always reflected on the characteristics of products, so that the yield of the products has been by no means high. In addition, this low yield has caused the increase of the cost of final products.